The subject matter disclosed herein generally relates to cooling flow in airfoils of gas turbine engines and, more particularly, to airfoil turn caps for cooling flow passages within airfoils in gas turbine engines.
In gas turbine engines, cooling air may be configured to flow through an internal cavity of an airfoil to prevent overheating. Gas temperature profiles are usually hotter at the outer diameter than at the inner diameter of the airfoils. In order to utilize cooling flow efficiently and minimize heat pickup and pressure loss, the cross-sectional area of the internal cooling flow may be configured to vary so that Mach numbers remain low where heat transfer is not needed (typically the inner diameter) and high Mach numbers where heat transfer is needed (typically the outer diameter). To do this in a casting, the walls of the airfoils tend to be thick in some areas and thin in other areas, which may add weight to the engine in which the airfoils are employed. Previously, baffles have been used to occupy some of the space within the internal cavity of the airfoils, referred to herein as “space-eater” baffles. The baffles extend from one end of the cavity all the way through the other end of the cavity within the airfoil. This configuration may result in relatively high Mach numbers to provide cooling throughout the cavity. Further, such configuration may provide high heat transfer, and pressure loss throughout the cavity.
In order to achieve metal temperatures required to meet full life with the cooling flow allocated, the “space-eater” baffles are required to be used inside an airfoil serpentine cooling passage. The serpentine turns are typically located outside gas path endwalls to allow the “space-eater” baffles to extend all the way to the gas path endwall (e.g., extend out of the cavity of the airfoil). However, because the airfoil may be bowed, the turn walls must also follow the arc of the bow to provide clearance for the “space-eater” baffles to be inserted. During manufacture, because the wax die end blocks do not have the same pull direction as the bow of the airfoil, the turn walls cannot be cast without creating a die-lock situation and trapping the wax die.
Thus it is desirable to provide means of controlling the heat transfer and pressure loss in airfoils of gas turbine engines, particularly at the endwall turn for serpentine gas paths.